Antivibration unit of a portable handheld work apparatus

ABSTRACT

An antivibration unit of a portable handheld work apparatus includes a leg spring ( 3 ) having at least one wire turn ( 5 ) and at least one first wire leg ( 6 ). The wire turn ( 5 ) extends about a turn or coil axis ( 4 ) and is attached at the first component assembly ( 1 ) and the first wire leg ( 6 ) extends outwardly and tangentially from the wire turn ( 5 ). A wire leg end ( 7 ) of the wire leg ( 6 ) is attached to the second component assembly ( 2 ).

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority of German patent application no. 102004 055 758.6, filed Nov. 18, 2004, the entire content of which isincorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to an antivibration unit of a portable handheldwork apparatus such as a chain saw, cutoff machine or the like forproviding a vibration decoupling connection of two component assembliesof the work apparatus.

BACKGROUND OF THE INVENTION

Portable handheld work apparatus are held and guided by an operator atone or several handles during operation. The drive motor and a tooldriven by the drive motor generate vibrations which are transmitted tothe handles and from there to the hands of the operator. For precise andnon-tiring work, a lowest possible vibration level in the area of thehandles is strived for.

A great many antivibration units are known for the vibration decouplingconnection of two component assemblies of the work apparatus, such as amotor assembly and a handle assembly. The use of rubber elements asantivibration elements is widespread. These rubber elements are matchedto the vibration behavior of the work apparatus with respect to theirstiffness and their material damping. The high transverse contractionnumber of the rubber material leads to a high transverse expansionduring an axial loading of the rubber antivibration element for which acorresponding structural space must be made available. The spring/dampercharacteristic of the rubber material changes with the excitationfrequency which operates thereon. An increase of the dynamic stiffnessoccurs with increasing excitation frequency. A static configuration isto be selected, which is very soft at rest without influence of thedynamic stiffness increase, in order to achieve an adapted, adequatelysoft matching adapted to the operating frequencies of the workapparatus. The low static stiffness can act disadvantageously on theguiding accuracy of the work apparatus. A compromise between guidingaccuracy and vibration decoupling has to be found in the configuration.

Furthermore, antivibration elements in the form of a spiral spring madeof steel wire are known. A matching of the vibration system iscomparatively simple because of the linear spring characteristic whichis essentially independent of frequency. However, the large requiredaxial space needed for the spring is disadvantageous.

SUMMARY OF THE INVENTION

It is an object of the invention to provide an antivibration unit of aportable handheld work apparatus having good vibration decouplingcharacteristics while at the same time requiring less space foraccommodating the same.

The antivibration unit of a portable handheld work apparatus of theinvention is for connecting first and second component assemblies of thework apparatus to decouple vibrations between the component assemblies.The antivibration unit includes: a leg spring having at least one wireturn defining a coil axis; the wire turn being attached to the firstcomponent assembly; the leg spring further having a first wire legprojecting outwardly from the wire turn; and, the first wire leg havingan end portion attached to the second component assembly so as to causethe leg spring to be subjected to load in the manner of a flexural barduring operation of the work apparatus.

An antivibration unit having a leg spring is proposed. The leg springhas at least one wire turn which runs about a turn or coil axis and isattached to a first component assembly. Furthermore, the leg spring isprovided with at least one first wire leg projecting outwardly away fromthe wire turn. The end of this wire leg is attached to a secondcomponent assembly. The wire leg preferably projects tangentially fromthe wire turn. A vibration-caused relative displacement of the twocomponent assemblies is transmitted by means of the wire leg to the wireturns which are loaded in the peripheral direction. The wire turns canbe wound tightly one against the other because of the absence of axialload whereby a very small axial structural space is required. Thetangential forces are introduced via the wire leg and cause a bendingload of the wire material in the wire turns. This bending load manifestsitself in a comparatively small oscillating increase or decrease of theturn diameter. Only a small structural space is required also in aradial direction. The wire turns require only one structural space inradial direction. A small radial play releases the oscillating diameterchanges. The length of the wire leg, the wire diameter and especiallythe number of wire turns can be adapted in a small structural space insuch a manner to the occurring vibration loads that stiffness and springdisplacement are associated with a low material loading of theantivibration unit.

In an advantageous further embodiment of the invention, the at least onewire turn is held on a lug extending along the turn or coil axis andengages around the lug with radial play. With the lug, simple andeffective means are formed for guidingly attaching the wire turns inradial direction. The radial play between the wire turns and the lugpermits a bending load of the turn packet in the peripheral direction insuch a manner that the turn package can freely contract in radialdirection. The wire turns are not hindered in their spring behavior.

In a further practical embodiment of the invention, the at least onewire turn is held on the lug in an axial direction form tight betweentwo wall sections. With simple means, an axial securing of the wireturns is formed without affecting its spring action.

At the end of the wire leg, a bearing pin for attaching the wire leg endto the second component assembly is arranged at right angles to thecorresponding first wire leg and axially parallel to the turn axis. Thebearing pin is provided for the rotatable journalling in the secondcomponent assembly, for example, in a handle. The rotatable journallingof the bearing pin permits an unhindered deflection of the wire legwithout affecting the spring damping ratio and without mechanicaloverloading at the attachment point of the second component assembly.

The bearing pin is configured as a snap pin and permits a simpleassembly without tools.

In an advantageous embodiment of the invention, at least a partialregion of the first wire leg is held in a guide which holds the firstwire leg in axial direction and enables it to move in a directionperipheral to the turn or coil axis. The first wire leg is held in theguide only with a base section close to the turns. The guide permits aprecise decoupling of the vibration loading tangentially to the turnaxis from vibration loads in axial direction. Depending upon theconfiguration of the guide, the antivibration element can be rigid inaxial direction. In a guide, which is limited to the turns-near basesection, the unsupported end of the wire leg, which lies outwardly,effects a stiffly designed decoupling as a consequence of its ownyielding. The bending deformation of the wire leg is limited to thesection between the introduction of force and the guide without beingtransferred to the wire turns as a consequence of the support action ofthe guide. An antivibration element is formed, which exhibits differentstiffnesses or transmitting characteristics in two different, mutuallyperpendicular directions which are decoupled from each other. An adapteddirection-independent vibration decoupling can be provided in dependenceupon operating loads of the work apparatus which are different in sizeand direction.

A holding section of the spring leg lies opposite to the wire leg end.This holding Section extends axially parallel to the turn axis and ispreferably held form tight in the first component assembly. The holdingsection engages over the wire turns on the outer side extending axiallyparallel to the turn axis. A simple reliable fixation of the leg springin the peripheral direction is formed which is in a position to reliablytake up the forces in the peripheral direction with these forces beingintroduced from the first wire leg. The axially parallel course of theholding section effects an additional slight yielding with which bearingtolerances can be compensated during assembly. The course of the holdingsection leads outside over the wire turns. The packet of wire turns canlie flat and tight directly against that wall on which also the holdingsection is attached without it being necessary to bend over the holdingsection at too tight a radius.

Between the wire turns and the above-mentioned wire holding section, asecond wire leg is provided which can contribute to accommodating theform changing energy in the spring material. The second wire legprojects outwardly especially tangential to the wire turns.

In an advantageous embodiment, the leg spring is mounted to lie in thedirection of the main thrust forces of the work apparatus with the legspring being in its direction running in the peripheral direction to theturn axis and standing at right angles to the first wire leg. It ispractical that the leg spring is mounted in a direction of lower thrustforces of the work apparatus with its axial direction pregiven by theturn axis. The spring action of the wire turns adjusts in the directionof the main thrust forces. There result also lower material tensions athigh deflection forces. The spring action of the antivibration unit islimited in the direction of lower thrust forces to the deformation ofthe first wire leg between its guide and the introduction of force atits wire leg end. The leg spring acts here as a flexural bar wherein thepermissible tension level is not exceeded as a consequence of the slightthrust forces. The remaining spatial direction is advantageously adirection without thrust forces. This direction lies approximatelycoaxially to the first wire leg in which the leg spring has nosignificant yielding. A residual yielding is present as a consequence ofthe radial play between the wire turns and the inner-lying lug. Toaccommodate forces in this direction, springs, which are spatiallyseparated, elastic stops or separate antivibration elements can bemounted.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described with reference to the drawingswherein:

FIG. 1 is a perspective exploded view showing the essential componentsof the antivibration unit of the work apparatus of the invention;

FIG. 2 is a front elevation view of the arrangement of FIG. 1 showingdetails of wire turns guided on a lug;

FIG. 3 is a plan view of the arrangement shown in FIGS. 1 and 2 in theassembled condition of component assemblies showing details of a guidedbase section of a first wire leg; and.

FIG. 4 is a schematic representation of the work apparatus of theinvention showing the component assemblies thereof interconnected by theantivibration unit.

DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION

FIG. 1 shows a perspective exploded view of an antivibration unit forthe vibration decoupling connection of two component assemblies (1, 2)of a portable handheld work apparatus. The component assemblies (1, 2)are indicated schematically.

The antivibration unit is also shown in FIG. 4 wherein it is identifiedby reference numeral 31. The work apparatus also comprises the twocomponent assemblies (1, 2) and the work apparatus is identified byreference numeral 30.

The work apparatus is especially driven by an internal combustion engineand can be a motor-driven chain saw, cutoff machine, hedge trimmer,blower/suction apparatus or the like. The first component assembly 1can, for example, be a motor housing having a drive motor mountedtherein. The second component assembly 2 can, for example, be a handlewhich is vibration decoupled from the motor housing by means of theantivibration unit shown.

The antivibration unit includes a leg spring 3 which is bent from steelwire running between a first end 26 and a second end 27. The leg spring3 comprises a first wire leg 6, wire turns 5, a second wire leg 17 and aholding section 16. The first wire leg 6 borders on the first end 26 andthe wire turns 5 are wound cylindrically about a turn or coil axis 4.The second wire leg 17 lies in the region of the second end 27 and theholding section 16 borders on the second end 27. Along its course fromthe first end 26 to the second end 27, the spring wire of the leg spring3 passes from the first wire leg 6 into the turns 5 and from there intothe second wire leg 17 and thereafter into the holding section 16.

A cylindrical lug 8 is attached to the first component assembly 1. Thewire turns 5 are pushed onto the lug 8 with a slight radial play. Inthis way, the turn axis 4 of the cylindrical packet of wire turns 5 liescoaxially to the lug 8. The wire turns 5 lie one against the other inthe axial direction 14 pregiven by the turn axis 4.

The second leg 17 lies between the wire turns 5 and the holding section16 and extends linearly starting from the wire turns 5. The second wireleg 17 projects outwardly tangentially to the wire turns 5. The wire leg17 can also be bent over outwardly with a radial directional component.The transition of the wire turns 5 to the second wire leg 17 as well asthe wire leg 17 itself lie, with respect to the axial direction 14, onthe side of the packet of wire turns 5 which faces away from the firstcomponent assembly 1. An axial spacing is formed from the second wireleg 17 to the first component assembly 1. The second wire leg 17 is bentover at right angles to a holding section 16 in a direction of its freeend. The holding section 16 runs axially parallel to the turn axis 4radially on the outside of the wire turns 5 in the direction of thefirst component assembly 1. The holding section 16 extends radially onthe outside beyond the axial length of the packet of wire turns 5. Theholding section 16 is inserted with the second end 27 into acorresponding opening of the first component assembly 1 and is held formtight in the peripheral direction referred to the turn axis 4.

To assemble the leg spring 3, the leg spring can be pushed onto the lug8 parallel to the turn axis 4. The holding section 16 is introduced atthe same time into the corresponding opening of the first componentassembly 1. Thereafter, a holding element 21 is attached to the lug 8.Respective wall sections (9, 10) are provided on the first componentassembly 1 and at the holding element 21. The packet of wire turns 5 isheld form tight in axial direction between the wall sections (9, 10). Intotal, the leg spring 3 is thereby completely attached to the firstcomponent assembly 1 and is fixed in all spatial directions.

An embodiment can be practical wherein the second wire leg 17 isomitted. The holding section 16 can, for example, be bent in theopposite direction and be attached to the holding element 21. Likewise,it can be practical to configure the holding leg 16 bent radiallyinwardly and held in a radial slot of the lug 8. In lieu of theattachment of the wire turns 5 on the lug 8, also an outside guide ofthe wire turns 5 can be practical, for example, a sleeve-shaped guide.By way of example, approximately two wire turns are shown. Dependingupon the operating loads to be expected and the given geometric boundaryconditions, any number of wire turns 5 for adapting the vibrationperformance of the antivibration unit can be practical.

The first wire leg 6 lies on the axial end face of the wire turns 5referred to the direction of the turn axis 4 and opposite to the secondwire leg 17. The first wire leg 6 extends in tangential directionstarting from the wire turns 5 outwardly in a direction of the secondcomponent assembly 2. The first wire leg 6 can also be bent overoutwardly with a radial component. In the embodiment shown, the wire leg6 runs approximately at right angles to the second wire leg 17. Therecan also be a different angle position between the two wire legs (6,17). A wire leg end 7 of the first wire leg 6 lies in the region of thefirst wire end 26. A support part 24 is attached to the wire leg end 7and this support part 24 is provided for attaching the wire leg end 7 tothe second component assembly 2. A support pin 11 is formed at thesupport part 24 with this support pin extending at right angles to thefirst wire leg 6 and axially parallel to the turn axis 4. The supportpin 11 can, for example, be formed by a bent-over end of the first wireleg 6. In the embodiment shown, the support pin 11 is configured as asnap pin for latching attachment to the second component assembly 2. Forforming the snap pin, two spring latches 18 are provided with each latchhaving a formed-on latch nose 19. The spring latches 18 are separatedfrom each other by means of a slit 20. The latch nose 19 can be insertedwithout tools into a suitable holding opening of the second componentassembly 2, for example, a handle. The slit 20 permits an elasticdeformation of the spring latches 18 relative to each other whereby thelatch noses 19 can be inserted. The elastic configuration of the springlatches 18 thereafter effects a spreading of the latch noses 19 wherebythe wire leg end 7 is attached form tight to the second componentassembly 2 in axial and radial direction referred to the support pin 11on the second component assembly 2. The support pin 11 is circular incross section and permits a rotational movement about its longitudinalaxis when mounted. A free deflection of the first wire leg 6 in aperipheral direction to the turn axis 4 is ensured. The peripheraldirection is indicated by a double arrow 13.

Guide surfaces (22, 23) are formed on the holding element 21 and thefirst component assembly 1, respectively. These guide surfaces form aguide 12 for a part region of the first wire leg 6. In the assembledstate, the wire leg 6 is so held in the guide 12 or between the guidesurfaces (22, 23) that the wire leg 6 is held approximately free of playin the axial direction 14 pregiven by the turn axis 4. The first wireleg 6 is freely moveable in the peripheral direction 13. Additionaldetails as to the operation of the guide 12 are provided in greaterdetail in connection with FIGS. 2 and 3.

FIG. 2 shows the arrangement of FIG. 1 in an end face view in thedirection of the turn axis 4. The antivibration unit of the invention ismounted in the work apparatus in such a manner referred to a coordinatesystem 28 that the first wire leg 6 lies parallel to the X-axis and theturn axis 4 lies parallel to the Z-axis (FIG. 3) of the coordinatesystem 28. The direction X of the coordinate system 28 is a directionwithout thrust forces of the work apparatus while the direction Yindicates the direction of the main thrust forces of the work apparatus.In the arrangement of the antivibration element shown relative to thecoordinate system 28, the direction Y of the main thrust forces is atright angles to the first wire leg 6 and to the turn axis 4. Amechanical load in the main thrust direction Y effects a relativedeflection of the second component assembly 2 relative to the firstcomponent assembly 1 in such a manner that the support part 24 movesstatically and/or oscillatingly in the peripheral direction to the turnaxis 4 with the peripheral direction being indicated by the double arrow13. The first wire leg 6 experiences bending in the peripheral direction13. The main part of the bending deformation in the same directionoccurs in the wire turns 5 which expand or contract radially referred tothe turn axis 4. A further lesser bending component in the samedirection arises in the second wire leg 17. The guide 12 lies with itssurfaces parallel to the direction of the double arrow 13 whereby thedeflection of the wire leg end 7 is made possible in this direction.

FIG. 3 shows the arrangement of FIGS. 1 and 2 in plan view parallel tothe Y direction (FIG. 2). The holding element 21 is threadably fastenedto the lug 8 (FIG. 1) by a threaded fastener 25 and is thereby part ofthe first component assembly 1. The wire turns 5 are held form tight inthe axial direction 14 between the first component assembly 1 and theholding element 21. The two guide surfaces (22, 23) lie slidingly atleast approximately free of play against a base section 15 of the firstwire leg 6. The guide surfaces (22, 23) and the base section 15 extend,referred to the axial direction of the first wire leg 6, over a shortregion close to the wire turns 5. Accordingly, the first wire leg 6 liesin the guide 12 only with its turns-near base section 15. This permits ayielding of the first wire leg 6 between the guide 12 and the wire legend 7 in a direction Z of lower thrust forces of the work apparatus.

Smaller relative displacements of the second component assembly 2 withrespect to the first component assembly 1 can adjust in the direction Zstatically and/or dynamically. The holding of the base section 15between the guide surfaces (22, 23) effects a support in the axialdirection 14 and the forces in the Z direction are held away from thewire turns 5. Loads in the Y direction (FIG. 2) and the Z direction aretaken up independently of each other and decoupled from each other. Inboth directions, a differently stiff designed vibration decoupling ofthe two component assemblies (1, 2) results. It can be practical topermit the guide 12 to extend over the entire length of the first wireleg 6 whereby the arrangement becomes rigid in the Z direction. Avibration decoupling of the component assemblies (1, 2) is then givenonly in the Y direction (FIG. 2).

It is understood that the foregoing description is that of the preferredembodiments of the invention and that various changes and modificationsmay be made thereto without departing from the spirit and scope of theinvention as defined in the appended claims.

1. A work apparatus comprising: a first component assembly and a secondcomponent assembly; and, an antivibration unit connecting said componentassemblies to decouple vibrations between said component assemblies;said antivibration unit comprising: a leg spring having at least onewire coil extending about a coil axis; said wire coil having aperipheral direction lying in a plane perpendicular to said coil axis;said wire coil being attached to said first component assembly and saidwire coil having a plurality of wire turns and extending about said coilaxis; said coil axis defining an axial direction; said first componentassembly and said second component assembly being movable relative toeach other in said peripheral direction of said wire coil and in saidaxial direction; said leg spring having a tangential direction extendingperpendicular to said axial direction in a plane arranged approximatelyperpendicularly to said coil axis; said leg spring further having afirst wire leg projecting outwardly from said wire coil referred to saidcoil axis and projecting in said tangential direction and said firstwire leg extending in said plane arranged approximately perpendicularlyto said coil axis; said first wire leg having an end portion attached tosaid second component assembly so as to cause said leg spring to besubjected to a load in the manner of a flexural bar during operation ofsaid work apparatus so as to permit a vibration-caused relativedisplacement of said first and second component assemblies in saidperipheral direction to be transmitted via said first wire leg to saidwire turns and thereby load said wire turns in said peripheral directionto said wire coil; a guide for holding at least a segment of said firstwire leg; and, said guide not blocking said first wire leg in saidperipheral direction of said wire coil and said guide holding said firstwire leg against movement in said axial direction so that vibrationloads in said axial direction and in said peripheral direction areabsorbed essentially independently of each other with said vibrationloads in said axial direction being absorbed essentially by said firstwire leg between said guide and the location of the introduction offorce and said vibration loads in said peripheral direction being takenup essentially by said wire coil.
 2. The work apparatus of claim 1,further comprising: a lug disposed so as to extend along said coil axis;and, said wire coil being held on said lug.
 3. The work apparatus ofclaim 2, wherein said wire coil engages around said lug with radialplay.
 4. The work apparatus of claim 2, further comprising first andsecond wall sections disposed with respect to said wire coil so as tohold said wire coil form tight therebetween on said lug in the directionof said coil axis.
 5. The work apparatus of claim 1, further comprisinga support pin for attaching said end portion of said first wire leg tosaid second component assembly; and, said support pin being at rightangles to said first wire leg and axially parallel to said coil axis. 6.The work apparatus of claim 5, wherein said support pin is configured asa snap pin.
 7. The work apparatus of claim 1, wherein said segment is abase segment of said first wire leg close to said wire turn; and, saidguide holds said first wire leg only at said base segment.
 8. The workapparatus of claim I, said leg spring further having a holding sectionlying opposite said end portion and said holding section extendingaxially parallel to said coil axis.
 9. The work apparatus of claim 8,wherein said holding section is held form tight in said first componentassembly.
 10. The work apparatus of claim 9, wherein said holdingsection extends outside of and beyond said wire coil.
 11. The workapparatus of claim 9, wherein said leg spring includes a second wire legprojecting outwardly from said wire coil; and, said second wire leg isdisposed between said wire coil and said holding section.
 12. The workapparatus of claim 11, wherein said second wire leg extends tangentiallyto said wire turn.
 13. The work apparatus of claim 1, wherein said legspring has a direction which is at right angles to said first wire legand extends in a peripheral direction to said coil axis; and, said legspring is mounted with said direction thereof in a direction (Y) of thethrust forces of said work apparatus.
 14. The work apparatus of claim 1,wherein said leg spring has an axial direction which is pregiven by saidcoil axis; and, said leg spring is mounted with said direction in adirection (Z) of lower thrust forces of said work apparatus.
 15. Thework apparatus of claim 1, wherein said work apparatus is a workapparatus such as a chain saw, cutoff machine, brushcutter or ablower/suction apparatus.
 16. A work apparatus comprising: a firstcomponent assembly and a second component assembly; and, anantivibration unit connecting said component assemblies to decouplevibrations between said component assemblies; said antivibration unitcomprising: a leg spring having a wire coil defining a coil axis; saidwire coil having a peripheral direction lying in a plane perpendicularto said coil axis; said first and second component assemblies beingmoveable relative to each other in said peripheral direction; said wirecoil having a plurality of wire turns and being attached to said firstcomponent assembly and extending about said coil axis; said coil axisdefining an axial direction; said leg spring having a tangentialdirection extending perpendicular to said axial direction and in a planearranged approximately perpendicularly to said coil axis; said legspring being made of spring wire and further having a first wire legprojecting outwardly as a continuation of one of said turns from saidwire coil referred to said coil axis and said first wire leg extendingin said tangential direction and in said plane arranged approximatelyperpendicularly to said coil axis; said first wire leg having an endportion attached to said second component assembly so as to cause saidleg spring to be subjected to load in the manner of a flexural. barduring operation of said work apparatus with said load being applied tosaid first wire leg in said peripheral direction in said plane as wellas in said axial direction; and, all of said wire turns of said wirecoil of said leg spring being wound tightly one against the other andwherein all of said wire turns lie directly one against the other insaid axial direction of said coil axis so as to cause mutually adjacentones of said wire turns to touch each other in the unloaded state ofsaid leg spring so as to permit said wire coil to absorb essentiallyonly that portion of said load acting in said peripheral direction insaid plane and thereby providing a compact configuration of said wirecoil in said axial direction.